In order to characterize a component of an optical system it is often necessary to apply a light beam of varying power to the system. The performance of the component may be characterized by observing its performance under different light power conditions. In this manner, an attenuated laser light beam may be used in the characterization of components such as receiver diodes, transmission paths and light amplifiers. Beam attenuation may also be used to simulate transmission paths of different lengths.
An optical attenuator may consist of a thin glass wafer coated with an optically attenuating material Unfortunately, this type of attenuator often causes reflection and undesired modulation of the light beam due to superposition of the reflected light beams onto the primary beam.
In accordance with the illustrated preferred embodiment of the present invention an optical attenuator provides variable attenuation without undesired modulation. The attenuator has an uncoated incoming surface which is orthogonal to the light beam. The outgoing surface is coated with an optically attenuating material and is inclined relative to the incoming surface so that light reflected at the outgoing surface is reflected away from the optical path of the incoming beam. The optical density of the attenuating coating varies with the angle of rotation of the attenuator. The coating may form an attenuation ring whose attenuation rises continuously over the angular range of zero to 360 degrees or less. During use, the attenuator may be rotated a pre-determined amount to cause a pre-determined amount of attenuation. The correspondence of angle of rotation and attenuation may be stored in a memory so that rotation may be controlled by a microprocessor.